Nonreflecting coating for galss



Jan.z7, 1942, H. w. vQKEs 2,271,239V A A I kNONREFLEC'I'ING COATING FORGLASS Filgd Sept. 28. 1940 ATTORNEY I HuwARD Qw. vnKEE INI/ENTORv i4Patented Jan. 27, 1942I i UNITED ',sTATEs PATENT OFFICE 2,271,231; v l

NONREFLEC'IING COATING FORi GLASS. v Howard W. Vokes, Rochester, N. Y.,vassignory vto Eastman Kodak Company, Rochester, N. Y., -l a corporationof New Jersey Y A Application september 2s, 1940, serial 358,850l l sclaims'.

This invention relates to apparatus and processes forcoating the surfaceof glass withinterference layers to prevent Fresnel reflections.

(ci. en -12.2)

' usually perform this cleanup after every half One form of reflectionobviatlng layer, namely` metallic fluoride on glass, ha'sbeen proposedby Professor Strong in the Journalof the Optical 73, wherein he refersto the'max'ima and minimaof the reflection as the film thickness variesand points out that the minima isfz'ero only. when the index of thecoating is thel square root of the index ofthe glass, making his twointerface reflections equal. The presentinvention relates to apparatusfor coating the lenses accordingl to Strongs process or according to'anyof the modifcations thereof, of which manyhave been proposed.

It isjan objectof the invention to provide an apparatus whereby coatingsmay be made more accurately and more quickly than hitherto.

It'is an object of the invention to provide` apparatus which is easy toclean between consecutive coatings.

It is an object'of. one embodiment of thei invention to reducethejarea.which has to be cleaned between coatings.,V l

It is the ultimate object of the invention to speed up the process whicheliminates uneven coatings such as those which result when flakes of thefluoride which have previously been deposited on the instrument breakloose therefrom and fall to the surface of the glass which is supposedto receive the coating.

In the practice of coating processes such' as 'described by Strong', alens, or group of lenses,

is suitably mounted in a bell Jar at a4 predetermined distance from andin unobstructed view viewing the operation. However this troubleis notas serious as is the fact that the corresponding coating of the metalsurfaces is liable to flake off and to spoil the coating of one or moreofr the lenses.

Therefore, the inside of the bell jarand particularly the metal surfacesof the container or lAccording tojthe invention, I have remediedthis-trouble and' speeded up 4the clean-up .proc-- ll "ess,v until the4time consumed .i'S practically neglidozen or so batches. I have foundthat the coating can be removed fairly easilyfrom.A the glass, ibut thatit adheres tenaciously to some. points on the metal.' only to flake oilduring subsequent gible, b y'plating practically .all the metal surfacesin the container with v'nickel or chromium, `preferably the latter. The.metal surfaces' should besrnooth (highly polished)` before plating.v Thel5 chromium plated surface .cleans .even easier than ly on areas inunobstructed view of the filament,

it'visthosexareas ofthe. metal surfaces which have the greatest need forthe chromiumplating. Generally I plate every .metal :surface that `goesinside the. bell jar 'and that-can beplatedw Y in'a reasonable manner.`

' According to one embodiment .of 'theinventiom I further reduce thetime consumed in clean-'up by reducing the areajof thesurfaces which arein unobstructed view ofthe filament." The lenses are usually-below the'la'mentand of course' nothing must be placed between them ani-i thefilament. By placing a shield in the form' of an inverted glass. beakerover the filament, the fluo# ride coating is prevented fromy reachingthe top of the bell jar and is restricted to the inside of the beaker,the lens and surrounding support` v and possibly to a narrow band aroundthe bell jar itself which band can be viewed by the filament between thesupport and the rim ofthe in-A verted beaker. With this arrangement, thetransparency of the top of the bell jar is never spoiled and by merelyputting in aclean beaker after every few coating runs, the visibility ofthe filament is assured. lIi? lenses are held both above and below thefilament, as described in copending application Serial No. 358,846 filedby Daniel B. McRae concurrently herewith, the

shield should be a cylinder. 'I'hus, the shield is close to the sides ofthe filament which sides are the ones not facing the lenses beingcoated. The shield is preferably transparent.

Other objects and advantages of the invention will be apparent from thefollowing description whenread in connection with the accompanyingdrawing, in which: f

Fig. 1 is a cross section in elevation of apparatus' incorporating theinvention. Y l

Fig. 2 is a horizontal cross section of the apparatus shown in Fig. 1.

In Fig. 1 aV bell jar I 0 supported on a metal plate Il is provided witha circular strip of rubber I2 as a seal and may be evacuated through apipe I3 by a vacuum pump not shown. .A cap I4 for the pipe I3 isprovided with openings I5 through which the air from the bell Jar I lmay be evacuated.

Positioned in this bell jar is a framework consisting of three legs i8carried by a ring I8,and. supporting three similar legs I1 carried by aring I9. The lower half of this framework made up of the legs I8 andring I8 supports a spherical disk 20 by means of three recessed portions2| in the legs IG. 'I'his spherical disk carries lenses 22 as shown, thesurfaces of which are to be coated with a non-reflecting layer.

The upper half of the framework consisting of the legs i1 and the ringI9 carries two cross members 23 as best shown in Fig. 2, to which bymeans of bolts or rivets 25 are attached two insulating cross arms 24 onwhich is supported a filament 26. This lament is to carry the fluorideduring the evaporation thereof. Wires 21 carrying the necessary currentto the filament 26 connect this filament through suitable insument 26travels in substantially straight lines outward from the filament andcoats any surface in unobstructed view of this filament. Incidentallysome of the materialseems to get around onto other surfaces which arenot in unobstructed view of the filament, but this eect is practicallynegligible. Thus not only the surfaces of the lenses 20 receive thefluoride coating, but also the surface of the metallic shell 20, theinside surface of the legs I6 and Il, the inside surface of the ring I9,certain surfaces of the cross-bars 23 and 24 and part of the innersurface of the bell jars l0. Since the shell 20 does not come all theway up to the ring I 9, a band 3i on the inner surface of the bell jarI0 receives considerable coating. According to the invention, all of themetallic surfaces in unobstructed view of the filament 26, (or betterstill practically all the metal surfaces exposed inside the `containerI0) are plated with chromium or nickel. This includes the inside surfaceof the ring I9, the inside surfaces of the legs i6 and i1 and the insidesurface of the shell 20 and the` surfaces of the cross arms 23.

If only the elements so far described in connection with the drawing,were used, the upper portions of the bell jar I0 would become coated andwould require frequent cleaning if the process is to be easily observed.Because of its size, the upper portions of the inside surface of thebell jar l0 are not easy to reach and are hence difficult to clean.According to a preferred embodiment of the invention, the coating ofthis portion of the bell jar is prevented and the total areas requiringcleaning are considerably reduced by placing a beaker 3l in an invertedposition on the cross arms 23. This beaker acts as a shield and may bereplaced after every two or three coatings, by a clean one and hence thetotal elapsed time of clean-up is'reduced to a minimum.

By my invention, the total clean-up time is reduced from abouthalf anhour to a minute or so and thus the cost of coating lenses isconsiderably reduced.

Having thus described my invention, I wish to point out that it is notlimited to this specific structure, but is of the scope of the appendedclaims. l

What I claim and desire to secure by Letters Patent of the United Statesis:

1. Apparatus for holding lenses during surface coating thereof with afluoride, comprising a container adapted to be` evacuated, means in thecontainer for the vaporization of the fluoride, means for supporting alens inside the container, to receive the fluoride coating saidcontainer and supporting means consisting at least partly of metal, themajor portion of the surfaces of said metal which are exposed insidesaid container being smooth and plated with a metal from the groupconsisting of chromium and nickel.

2. Apparatus according to claim 1 in which the plated metal is chromium.

3. Apparatus for holding lenses during surface coating thereof with afluoride, comprising a container, a filament supported inside thecontainer for holding and vaporizing the uoride for the coating andmeans for supporting a -lens in the container in unobstructed view ofsaid filament, the container and said supporting means consisting atleast partly of metal and all surfaces of the metal which are in view ofthe filament being smooth and plated with a metal from the groupconsisting of nickel and chromium.

4. Apparatus ,according to claim 3 in which the plated metal ischromium.

5. Apparatus for holding lenses during surface coating thereof by theevaporation of a iiuoride thereon, comprising a container adapted to beevacuated," a filament supported inside the container forv holding thefluoride, and means for supporting a lens in the container inunobstructed view of said lament, the supporting means and containerbeing made of metal and glass and all surfaces of the metal which are inview ofthe l'ament being smooth and plated with a metal from the groupconsisting of nickel and chromium.

6. Apparatus for holding lenses during surface coating by theevaporation of a fluoride thereon comprising a container adapted to beevacuated, a filament supported inside the containerv for holding theu'oride, and means for supporting a lens in the container inunobstructed view of said filament, the supporting means and containerbeing made of metal and glass and all surfaces of the metal which are inunobstructed view of the lament being smooth and chromium plated.

HOWARD W. VOKES.

